Apparatus for converting pressure energy to thermal energy

ABSTRACT

Apparatus is provided for converting pressure energy to thermal energy which includes a means for directing a high velocity flow of a compressible fluid at the open end of a resonance tube assembly. The resonance tube assembly includes a plurality of resonance tubes, the inlet ends of which are juxtaposed and separated by a knife-edge wall. The provision of the knife-edge wall common to the passages of the resonance tubes provides for the generation of oscillations of gas within each tube which are out of phase with oscillations in other tubes. The closed end of each resonance tube preferably embodies a mass of metallic material to define a &#39;&#39;&#39;&#39;heat sink&#39;&#39;&#39;&#39; for retaining thermal energy in that portion of the tube adjacent the closed end. The &#39;&#39;&#39;&#39;heat sink&#39;&#39;&#39;&#39; portion of the tube is thermally isolated from the remaining portions of the tube by a thin walled tube section which retards the flow by conduction of thermal energy away from the closed end of the tube.

United States Patent Schmidlin APPARATUS FOR CONVERTING PRESSURE ENERGY TO THERMAL ENERGY Inventor: Albertus E. Schmidlin, Caldwell,

Assignee:

represented by the Secretary of the Army Filed: April 30, 1971 Appl. No.: 139,111

US. Cl "432/227, 432/266, 432/T Int. Cl .Q ..F27h 17/00 Field of Search ..263/ l, 52; 126/247 References Cited UNITED STATES PATENTS 5/1953 Lewis, Jr. ..l26/347 X 9/1961 Bodine, Jr. ..l26/247 X The United States of America as Primary Examiner-John J. Camby Attorney-Edward J. Kelly, Herbert Her] and Victor Erkkila [5 7] ABSTRACT Apparatus is provided for converting pressure energy to thermal energy which includes a means for directing a high velocity flow of a compressible fluid at the open end of a resonance tube assembly. The resonance tube assembly includes a plurality of resonance tubes, the inlet ends of which are juxtaposed and separated by a knife-edge wall. The provision of the knife-edge wall common to the passages of the resonance tubes provides for the generation of oscillations of gas within each tube which are out of phase with oscillations in other tubes. The closed end of each resonance tube preferably embodies a mass of metallic material to define a heat sink for retaining thermal energy in that portion of the tube adjacent the closed end. The heat sink portion of the tube is thermally isolated from the remaining portions of the tube by a thin walled tube section which retards the flow by conduction of thermal energy away from the closed end of the tube.

17 Claims, 6 Drawing Figures APPARATUS FOR CONVERTING PRESSURE ENERGY T THERMAL ENERGY The invention described herein may be manufactured, used and licensed by and for the Government for Governmental purposes without the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION This invention relates to the field of apparatus for converting pressure energy to thermal energy. Specifically, this invention relates to resonance tubes for converting pressure pulses generated within a tube by a compressible fluid flowing at high velocity against an open end of the tube to thermal energy.

It is generally known by those skilled in the field of the present invention that a resonance tube or Hartmann generator, (see Richardson, E. G. and Myer, E. Technical Aspects ofSound, Vol. III, 1962, p. l38-l4l which in its simplest form consists of a cylindrical tube closed at one end and driven at the open end by a high velocity flow of gas, experiences an irreversible heating process adjacent the closed end of the tube. For certain combinations of gas supply, pressure and resonance tube dimensions, violent oscillations occur in the gas which produce an entropy rise through a shock wave.

It has been suggested that twin resonance tubes be used n combination in order to accomplish a more efficient transfer of energy from the flowing gas to the oscillating gas columns which are set up in the twin resonance tubes. Apparatus embodying this suggestion, however, have been complicated both structurally and operationally. Specifically, such apparatus have relied on control means such as fluid amplifiers and the like for establishing a coordination of operation between related resonance tubes. Such control means render the apparatus for conversion unduly complicated, sensitive and expensive and as such are undesirable. 7

SUMMARY OF THE INVENTION It is the principal object of the present invention, therefore, to provide a resonance tube apparatus for converting pressure energy to thermal energy, which apparatus requires no control elements or like devices to establish desired operating characteristics in the apparatus.

A further object of the invention is to provide an apparatus for converting pressure energy to thermal energy wherein the flowing gas is utilized to high efficiency in obtaining a high temperature at the closed end of the tube, and the tube is structured to obtain maximum thermal advantage of the system.

These objects and others not enumerated are achieved by the present invention, one embodiment'of which may include a first resonance tube having an open end and a closed end, at least one additional resonance tube disposed adjacent the first resonance tube and having an open end and a closed end, the open ends of the resonance tubes being juxtaposed, means for directing a high velocity flow of gas at the open ends of the resonance tubes for establishing a gas resonance therein, said gas resonance for generating thermal energy at the closed ends of the resonance tubes and means for retaining the thermal energy at the closed ends of the resonance tubes.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present invention may be had from the following detailed description thereof, particularly when read in the light of the attached drawings, wherein:

FIG. 1 is a perspective view, partially cutaway of apparatus structured according to the invention;

FIG. 2 is a side view, partially in section, of a nozzle for use with the apparatus of FIG. 1;

FIG. 3 is a side elevational view of the resonance tube assembly of the apparatus of FIG. 1;

FIG. 4 is a cross-sectional view through the plane 4 4 of FIG. 3;

FIG. 5 is a cross-sectional view through the plane 5 5 of FIG. 4; and 7 FIG. 6 is a cross-sectional view similar to the view of FIG. 5 but showing a three element resonance tube assembly.

DETAILED DESCRIPTION Referring to FIG. 1, an apparatus for converting pressure energy to thermal energy is shown and designated generally by the reference numeral 10.

Apparatus 10 comprises a generally U-shaped base 12 having a first upwardly extending support 14 and a second upwardly extending support 15. First upwardly extending support is provided with a longitudinally extending bore 16 through which is received a nozzle element 18. Nozzle element 18 is connected to a source (not shown) of pressurized gas, e. g., helium at room temperature and I20 P.S.I., whereby the pressurized gas can be caused to flow through the nozzle opening 19 of nozzle element 18 to establish the gas oscillations required in the resonance tube assembly during operation of the apparatus. Nozzle 18 is rigidly positioned within the bore of first upwardly extending support 14 by a set screw 17 which is disposed in an upwardly extending tapped bore in support 14.

Second upwardly extending support 15 is provided with a longitudinally extending bore 13 which is coaxial with the longitudinally extending bore 16 in first upwardly extending support 14. Mounted within bore 13 is aresonance tube assembly according to the invention designated generally by reference numeral 20. Resonance tube assembly 20 comprises a base section 22 and two tubular sections, each tubular section including a heat retaining element 24 and a spacer element 25. A vertically extending tapped bore is formed in second upwardly extending support 15 for receiving a set screw 26 to rigidly secure resonance tube assembly 20 within bore 13.

As noted above, resonance tube assembly 20 comprises a base section 22 and two tubular sections, each tubular section including a heat retaining element 24 and a spacer element 25. Referring particularly to FIGS. 3, 4 and 5, it can be seen that base 22 comprises a cylindrical block in which are formed two parallel adjacent passages 27 and 28 which extend longitudinally therethrough. First passage 27 has an inlet end 31 and an outlet end 32. Similarly, second passage 28 has an inlet end 33 and an outlet end 34. The cross-sectional configuration of each of passages 27 and 28 at their inlet ends 31 and 33, respectively, is rectangular. From their respective inlet ends 31 and 33 to their respective outlet ends 32 and 34, passages 27 and 28 are formed to change in cross-sectional configuration from rectangular to circular. The circular cross-section for resonance tubes of this invention is generally preferred because of ease of fabrication. However, non-circular shapes, e. g., oval and rectangular, are operative in the present invention and may be desirable for particular applications. Adjacent their outlet ends 32 and 34, each of passages 27 and 28 is provided with a shallow counterbore in which to receive spacer elements 25.

As can be best seen in FIG. 4, passages 27 and 28 share a common wall 36. The end of wall 36 adjacent the inlet openings 31 and 33 of passages 27 and 28 is tapered to define a knife-edge 38. As will be discussed in detail below, the provision of a knife-edge 38 is important to the operation of apparatus 10. Further, it should also be noted that although the remaining edges of the walls of passages 27 and 28 at inlet ends 31 and 33 are shown as being tapered to define knife-edges, this is a design choice which is not necessary to the concept of the present invention as shown in the embodiment of FlGS.1-5.

Heat retaining element 24 is cylindrical (although not limited thereto as noted above) having one end closed by an end wall 40. The inside diameters of elements 24 correspond to the inside diameters of spacer elements 25 and the diameters of passages 27 and 28 adjacent their outlet ends 32 and 34, respectively. The open ends of heat retaining elements 24 are provided with counter-bores 42 for rigidly receiving the ends of spacer elements 25. The outer surface of each heat retainer element 24 is relieved centrally to define a thin walled section 44, the purpose of which is discussed below.

With respect to the manufacture of the components of apparatus 10, it may be said that each of the elements may be manufactured from commercially available materials by known manufacturing and machining techniques. It has been found that stainless steel is an acceptable material for nozzle 18, base 22, spacer ele ment 25 and heat retainer element 24. It should be recognized, however, that many other materials are available which are capable of achieving the desired results.

Considering now the operation of apparatus 10, nozzle element 18 and resonance tube assembly are positioned in upwardly extending supports 14 and 15, respectively and secured by set screws 17 and 26. The proper separation of nozzle 19 from the inlet ends 31 and 33 of passages 27 and 28 is necessary in order to achieve resonance. It is to be understood, however, that a determination as to proper spacing is dependent upon the gas to be utilized, the dimensions of the'components and the desired results, and can be made using techniques which are generally known in this art.

With the elements properly positioned, a flow of pressurized gas, e. g., helium at 120 P.S.l. at room temperature is established through nozzle element 18. N02- zle opening 19 of nozzle element 18 is shaped and sized to permit discharge of the gas therethrough at approximately sonic speed whereafter the expansion of the gas upon being pressure-relieved causes a super-sonic velocity to be achieved in front of the end openings 31 and 33 of passages 27 and 28.

The direction of the high velocity gas against'the inlet openings 31 and 33 of passages 27 and 28 causes a jet edge tone and flow splitting effect at knife-edge 38 thereby causing an instability in the gas flow, which when combined with the tendency for periodic com-- pression and expansion waves to occur in each of passages 27 and 28, causes one of the passages 27 and 28 to receive more flowing gas than the other. The passage receiving more of the flowing gas increases in gaseous-density and pressure more quickly than the other and continues to so increase until the generated pressure is sufficiently high to cause a backflow of gas out of the passage. At this stage, the other passage is being filled with the flowing gas and, in fact, is being filled partially by spillage" or back-flowing gas from the adjacent passage. This spillage" effect, of. course, is an advantage because gas flowing from one passage to the other is effectively preheated and adds to the capability of the system for generating thermal energy.

Continued direction of the high velocity gas jet" against the inlet ends 31 and 33 of passages 27 and 28 continues the alternative filling and spilling of gas into and from the respective passages. In this regard, the filling and spilling cycles occur at very high frequencies (1,000 .u 15,000 cycles per second) and cause the generation of extremely high temperatures, e. g., over 2,000F., at the closed ends of the resonance tubes.

Considering now the heat retention capability of apparatus according to the invention, and with particular reference to FIG. 3, it can be seen that the closed ends of heat retainer elements 24 as well as end wall 40 are relatively thick in wall thickness, particularly as compared with thin wall portions 44. mass of metal at the closed ends of heat retainer elements 24 to act as heat sinks for retaining thermal energy generated by the high frequency oscillation of gas within the tubes. The thermal energy retention capabilities of the heat sink are augmented by the provision of thin wall sections 44 because the removal of metal occurrence of conduction of thermal energy away from the heat sink area.

The principles of the present invention are applicable to resonance tube assemblies comprising more than two resonance tubes. For example, and with reference to FIG. 6, there is shown the inlet end of a resonance tube assembly of an apparatus for converting pressure energy to thermal energy wherein three resonance tube structures are utilized. The structure of the apparatus in which tube assembly 120 is utilized is exactly the same as that shown in FIGS. 1-5 in every respect for the structure of the base section and for the fact that three resonance tubes are provided instead of two.

Referring to FIG. 6, therefore, there is shown for base section 122 of resonance tube assembly 120. Base section 122 is provided with three passages 124, 125 and 126 extending therethrough. Passages 124, 125 and 126 are provided with inlet openings 127, 128 and 129 and outlet openings 131, 132 and 133 respectively. The longitudinal axes of passages 124, 125 and 126 are disposed symmetrically about the longitudinal axis of base section 122. Further, the configuration of passages 124, 125 and 126 is transitional from being pie-shaped at inlet ends 127, 128 and 129 to being circular at outlet ends 131, 132 and 133.

Passages 124, 125 and 126 are juxtaposed and each shares at least one common wall with the other. More passages 124 and 125 are separated by a radially extending wall 136, passages 125 and 126 are separated by a radially extending wall 137, and passages 124 and 126 are separated by a radially extending wall 138. Each of the edges of walls 136, 137 and 138 at the inlet ends of the passages 124, 125 and 126, are tapered to define knife edges 14], 142 and 143 for achieving the jet edge tone and flow splitting effect which was discussed above with respect to apparatus 10.

The operation of an apparatus utilizing three resonance tubes rather than two is exactly the same as that discussed above with respect to the apparatus of FIGS. 1-5. The only difference is that the high velocity flow of pressurized gas is utilized with greater efficiency and greater thermal energy, and slightly higher end temperatures can be achieved.

It is considered to be evident from the foregoing that apparatus structured in accordance with the present invention present two advantages over the prior art. lnitially, the provision for achieving the jet edge tone and flow splitting effects which'provide for out of phase gas oscillation in adjacent resonance tubes eliminates the prior art requirement for specific means for phasing the gas oscillations. Secondly, the provision of a heat sink at the end of each resonance tube as well as the thermal isolation of the heat sink from the remaining apparatus structure permits the retention of thermal energy in the tube ends and thus improves the capability of the apparatus for achieving higher end temperatures. Energy conversion units of this type are useful for such functions as fuel igniters, igniters for solid propellant engines, thermal-electric generators and similar uses.

Although the principles of the present invention have been described in detail only with respect to two embodiments, it is considered to be manifest that many modifications and variations to describe the structure can be made without departing from the spirit and scope of the invention.

lclaim:

1. Apparatus for converting pressure energy to ther mal energy comprising,

a first resonance tube having an open end and a closed end;

at least one additional resonance tube disposed adjacent said first resonance tube and having an open end and a closed end, said open ends of said resonance tubes being juxtaposed;

means for directing a high velocity flow of gas at said open ends of said resonance tubes for establishing a gas resonance therein, said gas resonance for generating thermal energy at the closed ends of said resonance tubes.

2. Apparatus according to claim 1 wherein said juxtaposed open ends of said resonance tubes are separated by a common wall portion and said common wall portion is formed at its edge to define a knife edge.

3. Apparatus according to claim 1 wherein each said resonance tube includes a thick wall portion at the closed end thereof and a thin wall portion adjacent said thick wall portion.

4. Apparatus according to claim 1 wherein each said resonance tube includes a base section and a tube section, and each said tube section includes a thick wall portion at the closed end thereof and a thin wall portion adjacent said thick wall portion.

5. Apparatus according to claim 3 wherein said thick wall portion of each of said resonance tubes defines means for retaining said thermal energy at the closed ends of said resonance tubes.

6. Apparatus according to claim 4 wherein said base section of each resonance tube embodies said open end of said resonance tube, and wherein said open end of each resonance tube is rectangular in shape.

7. Apparatus according to claim 4 wherein the base section of each said resonance having one passage extending therethrough for each resonance tube.

8. Apparatus according to claim 6 wherein said resonance tube includes a passage extending through said base section, and said passage changes in crosssectional configuration from rectangular to circular from the inlet end to the outlet end thereof.

9. Apparatus according to claim 7 wherein each passage formed in said base section is bounded by walls and juxtaposed each other passage, and wherein each passage shares one wall with each other passage, the edge surfaces defining knife edges.

10. Apparatus according to claim 9 wherein each said passage changes in configuration from the configuration at the inlet end to a circular configuration at the outlet end thereof.

11. Apparatus for converting pressure energy to thermal energy, said apparatus including a means for directing a high velocity flow of a compressible fluid at the open end of a resonance tube assembly, wherein said resonance tube assembly comprises:

a first resonance tube comprising a base section and a tubular section having a closed end and an open end;

at least one additional resonance tube comprising a base section and a tubular section having a closed end and an open end;

a passage extending through each said base section, each passage including an inlet end and an outlet end, said outlet end of each said passage being joined to the open end of its corresponding tubular section, each said joined base and tubular sections cooperating to define said resonance tubes; and

heat sink means disposed adjacent the closed end of each said tubular section for retaining thermal energy.

12. Apparatus according to claim 11 including means formed on said tubular section adjacent said heat sink means for retarding the conduction of thermal energy away from said heat sink means.

13. Apparatus according to claim 11 wherein said inlet end of each said passage in said base is non-round in cross-sectional configuration, and wherein said outlet end of each said passage in said base is circular in cross sectional configuration.

14. and of said passage in said base of said first resonance tube is juxtaposed the inlet end of said passage in said base of said additional resonance tube.

15. Apparatus according to claim 14 wherein said passage in said base of said first resonance passage in said base of said additional resonance tube by a common wall, and further wherein said common wall defines a knife-edge at the inlet ends of said passages.

16. Apparatus according to claim 15 including means formed on said tubular section adjacent said heat sink means for retarding the conduction of thermal energy away from said heat sink means.

17. An apparatus according to claim 16 wherein said heat sink means comprises a thick wail section formed on the closed end of said tubular section and said means for retarding conduction comprises a thin wall portion of said tubular section. 

1. Apparatus for converting pressure energy to thermal energy comprising, a first resonance tube having an open end and a closed end; at least one additional resonance tube disposed adjacent said first resonance tube and having an open end and a closed end, said open ends of said resonance tubes being juxtaposed; means for directing a high velocity flow of gas at said open ends of said resonance tubes for establishing a gas resonance therein, said gas resonance for generating thermal energy at the closed ends of said resonance tubes.
 2. Apparatus according to claim 1 wherein said juxtaposed open ends of said resonance tubes are separated by a common wall portion and said common wall portion is formed at its edge to define a knife edge.
 3. Apparatus according to claim 1 wherein each said resonance tube includes a thick wall portion at the closed end thereof and a thin wall portion adjacent said thick wall portion.
 4. Apparatus according to claim 1 wherein each said resonance tube includes a base section and a tube section, and each said tube section includes a thick wall portion at the closed end thereof and a thin wall portion adjacent said thick wall portion.
 5. Apparatus according to claim 3 wherein said thick wall portion of each of said resonance tubes defines means for retaining said thermal energy at the closed ends of said resonance tubes.
 6. Apparatus according to claim 4 wherein said base section of each resonance tube embodies said open end of said resonance tube, and wherein said open end of each resonance tube is rectangular in shape.
 7. Apparatus according to claim 4 wherein the base section of each said resonance having one passage extending therethrough for each resonance tube.
 8. Apparatus according to claim 6 wherein said resonance tube includes a passage extending through said base section, and said passage changes in cross-sectional configuration from rectangular to circular from the inlet end to the outlet end thereof.
 9. Apparatus according to claim 7 wherein each passage formed in said base section is bounded by walls and juxtaposed each other passage, and wherein each passage shares one wall with each other passage, the edge surfaces defining knife edges.
 10. Apparatus according to claim 9 wherein each said passage changes in configuration from the configuration at the inlet end to a circular configuration at the outlet end thereof.
 11. Apparatus for converting pressure energy to thermal energy, said apparatus including a means for directing a high velocity flow of a compressible fluid at the open end of a resonance tube assembly, wherein said resonance tube assembly comprises: a first resonance tube comprising a base section and a tubular section having a closed end and an open end; at least one additional resonance tube comprising a base section and a tubular section having a closed end and an open end; a passage extending through each said base section, each passage including an inlet end and an outlet end, said outlet end of each said passage being joined to the open end of its corresponding tubular section, each said joined base and tubular sections cooperating to define said resonance tubes; and heat sink means disposed adjacent the closed end of each said tubular section for retaining thermal energy.
 12. Apparatus according to claim 11 including means forMed on said tubular section adjacent said heat sink means for retarding the conduction of thermal energy away from said heat sink means.
 13. Apparatus according to claim 11 wherein said inlet end of each said passage in said base is non-round in cross-sectional configuration, and wherein said outlet end of each said passage in said base is circular in cross sectional configuration.
 14. and of said passage in said base of said first resonance tube is juxtaposed the inlet end of said passage in said base of said additional resonance tube.
 15. Apparatus according to claim 14 wherein said passage in said base of said first resonance passage in said base of said additional resonance tube by a common wall, and further wherein said common wall defines a knife-edge at the inlet ends of said passages.
 16. Apparatus according to claim 15 including means formed on said tubular section adjacent said heat sink means for retarding the conduction of thermal energy away from said heat sink means.
 17. An apparatus according to claim 16 wherein said heat sink means comprises a thick wall section formed on the closed end of said tubular section and said means for retarding conduction comprises a thin wall portion of said tubular section. 